1. Field of the Invention
The present invention relates to a method of collecting data with respect to a group of injection molding machines which is suitably used in factories or the like equipped with a plurality of injection molding machines.
2. Description of the Relevant Art
Conventional factories equipped with a plurality of injection molding machines have an arrangement wherein LAN (local area network) systems are established, a collection is made by a direct numerical control computer system for various data with respect to an operational physical value of each injection molding machine, in particular, for data in connection with the pressure, velocity, temperature, time and the like each affecting a quality of an injection molding product. The collected data is operated to produce statistic values such as an average value, a maximum value, a minimum value, a variance and a range, based on which a quality control is performed. The systems of these kinds are known in the Japanese Patent Application Laid Open No. 143825/1990.
A method of collecting data using such LAN systems is in that various data detected from respective injection molding machines at every cycle (at every shot) have been transmitted to a direct numerical control computer system through a transmission line in real time, concurrently the direct numerical control computer receives such data to display the data for every injection molding machine or to perform filing them on a disk. Depending on a requirement, the data filed on the disk have been executed a statistic processing with respect to the injection molding machine and the database formation processing for a quality control and so forth so that the filed data are output as a substantial quality data of the injection molding together with a history of the injection molding process etc. This enables to collect information for a plurality of injection molding machines in real time, to obtain a large amount of data by realizing a higher capacity and an upgraded characteristic each of the computer memory, and to perform a complex processing on analysis and evaluation of the collected data. A quality control procedure in this case is thus graded up to ensure and facilitate the direct numerical control. In the LAN system, because a relatively more separated distance is required between the respective injection molding machines or between the direct numerical control computer system and the injection molding machine, then in general there are employed an optical communication system using optical fiber cables, a current loop system using electrical wire, and a radio communication system by a microwave, and due to the extended communication distance there is further employed a serial communication interfaces such as RS232C and RS422 each capable of reliably producing the data at a relatively lower cost.
The data in connection with the operational physical values of the molding machine used for the quality control include an injection primary pressure time, a measurement time, a screw position at the instant when the injection terminates, a cycle time and so forth, the number of those items described being relatively small (equal to ten items or below), however, the number of the items have now increased to twenty or more as a result of gradually fractionating due to a high grade of the quality control procedure. In addition, each of respective injection molding machines providing different products requires a different analysis from each other on a quality control therefor.
In this way, where the kinds of data to be communicated are increased to as many as twenty items, 128 bytes are required for transmission data including a transmission control code and command, a communication error control command and the like. Further, the transmission data of each injection molding machine incorporated into the LAN system is expanded to many divergences, for example, in addition, to a production control data, a status data of the injection molding machine, and an error generating data. This indicates a considerably large amount of data as a whole. With the serial communication interfaces used as described above, communication speeds of 4800 bps to 9600 bps are generally adopted, and therefore only a communication in the order of about 480 bytes to 960 bytes per second is available, or may be less in consideration of the processing time of the control devices with respect to the direct numerical control computer system and the respective injection molding machines.
The number of injection molding machines under the direct numerical control reaches generally at least to approximately ten sets, and not a few of injection molding machines with 3 to 4 second-cycles are produced by means of cycling up the machines.
As described above, when communicating the data including as many as twenty items at every cycle, a capability of the conventional method of data collection has been limited and resulted in a possibility to generate a cycle omission (dislocation of a cycle) because of difficulty to follow such a service speed in the data communication. The use of a particular communication dedicated device and a communication protocol, for example, Ethernet or the like having a communication speed of 10 mega-bps, are considered for the higher communication speed; however, it can not be employed in a practical use because of a considerably high cost.